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1、DRAFT FOR DEVELOPMENT DD ENV 12788:1998 Advanced technical ceramics Mechanical properties of ceramic composites at high temperature under inert atmosphere Determination of flexural strength ICS 81.060.99 Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 05:52:12 G
2、MT+00:00 2006, Uncontrolled Copy, (c) BSI DD ENV 12788:1998 This Draft for Development, having been prepared under the direction of the Sector Board for Materials and Chemicals, was published under the authority of the Standards Board and comes into effect on 15 July 1998 BSI 04-1999 ISBN 0 580 3001
3、3 7 National foreword This Draft for Development is the English language version of ENV 12788:1998. This publication is not to be regarded as a British Standard. It is being issued in the Draft for Development series of publications and is of a provisional nature because it is considered that furthe
4、r experience is required in its application before it is converted into a British Standard. It should be applied on this provisional basis, so that information and experience of its practical application may be obtained. Comments arising from the use of this Draft for Development are requested so th
5、at UK experience can be reported to the European organization responsible for its conversion into a European Standard. A review of this publication will be initiated 2 years after its publication by the European organization so that a decision can be taken on its status at the end of its three-year
6、life. The commencement of the review period will be notified by an announcement in Update Standards. According to the replies received by the end of the review period, the responsible BSI Committee will decide whether to support the conversion into a European Standard, to extend the life of the pres
7、tandard or to withdraw it. Comments should be sent in writing to the Secretary of BSI Technical Committee RPI/13, Advanced technical ceramics, 389 Chiswick High Road, London W4 4AL, giving the document reference and clause number and proposing, where possible, an appropriate revision of the text. A
8、list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “Internat
9、ional Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the ENV title page, pages 2 to 8 and a back cover. This standard has been updated (see copy
10、right date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.DateComments Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 05:52:12 GMT+00:00 2006, Uncon
11、trolled Copy, (c) BSI DD ENV 12788:1998 BSI 04-1999i Contents Page National forewordInside front cover Foreword2 Text of ENV 127883 Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 05:52:12 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: London
12、 South Bank University, London South Bank University, Tue Dec 12 05:52:12 GMT+00:00 2006, Uncontrolled Copy, (c) BSI EUROPEAN PRESTANDARD PRNORME EUROPENNE EUROPISCHE VORNORM ENV 12788 April 1998 ICS 81.060.99 Descriptors: Composite materials, reinforcing materials, technical ceramics, mechanical pr
13、operties, high temperature tests, test atmospheres, determination, flexural strength English version Advanced technical ceramics Mechanical properties of ceramic composites at high temperature under inert atmosphere Determination of flexural strength Cramiques techniques avances Proprits mcaniques c
14、omposites haute temprature sous atmosphre inerte Dtermination de la rsistance en flexion This European Prestandard (ENV) was approved by CEN on 27 June 1997 as a prospective standard for provisional application. The period of validity of this ENV is limited initially to three years. After two years
15、the members of CEN will be requested to submit their comments, particularly on the question whether the ENV can be converted into a European Standard. CEN members are required to announce the existence of this ENV in the same way as for an EN and to make the ENV available promptly at national level
16、in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the ENV) until the final decision about the possible conversion of the ENV into an EN is reached. CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finl
17、and, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Br
18、ussels 1998 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. ENV 12788:1998 E Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 05:52:12 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ENV 12788:1998 BSI
19、04-1999 2 Foreword This European Prestandard has been prepared by Technical Committee CEN/TC 184 “Advanced technical ceramics”, the secretariat of which is held by BSI. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to ann
20、ounce this European Prestandard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. Contents Page Foreword2 1Scope3 2Normative references3 3Principle3 4Def
21、initions and symbols3 4.1test temperature, T3 4.2maximum flexural force, Fm3 4.3flexural stress, 3 4.4flexural strength, f,m3 5Apparatus3 5.1Test machine3 5.2Test jig3 5.3Test chamber4 5.4Set-up for heating4 5.5Temperature measurement4 5.6Data recording system4 5.7Micrometers4 6Test specimens4 7Test
22、 specimen preparation4 7.1Machining and preparation4 7.2Number of test specimens5 8Test procedures5 8.1Test set-up: Temperature considerations5 8.2Test set-up: Other considerations5 8.3Testing technique5 8.4Test validity6 9Calculation of results6 9.1Test specimen origin6 9.2Flexural strength6 10Test
23、 report7 Figure 1 Articulation required for jigs8 Table 1 Recommended test specimen and span dimensions4 Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 05:52:12 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ENV 12788:1998 BSI 04-19993 1 Scope This European prestan
24、dard ENV 12788 specifies the conditions for determination of the flexural strength of ceramic matrix composite materials with continuous fibre reinforcement under three-point or four-point bending for temperatures up to 2 000 C under vacuum or a gas atmosphere which is inert to the material under te
25、st. This Prestandard applies to all ceramic matrix composites with a continuous fibre reinforcement, unidirectional (1D), bidirectional (2D), and tridirectional (xD, with 2 3), loaded along one principal axis of reinforcement. NOTE 1The use of these environments is aimed at avoiding changes of the m
26、aterial affecting its flexural strength caused by chemical reaction with its environment during the test. NOTE 2The method should not be used to obtain values of flexural strength for design purposes. 2 Normative references This European prestandard incorporates by dated or undated reference, provis
27、ions from other publications. These normative references are cited at appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to, or revisions of any of these publications apply to this European Prestandard only when incorporated in it by
28、 amendment or revision. For undated references the latest edition of publication referred to applies. ENV 843-5, Advanced technical ceramics Monolithic ceramics Mechanical tests at room temperature Part 5: Statistical analysis. ENV 12789, Advanced technical ceramics Mechanical properties of ceramic
29、composites at high temperature under air at atmospheric pressure Determination of flexural strength. EN 10002-2, Metallic materials Tensile testing Part 2: Verification of the force measuring system of the tensile testing machines. EN 60584-1, Thermocouples Part 1: Reference tables. EN 60584-2, Ther
30、mocouples Part 2: Tolerances. ISO 3611, Micrometer callipers for external measurement. 3 Principle A test specimen of specified dimensions is heated to the testing temperature. It is subsequently flexion loaded to fracture in such a way that failure occurs in tension or in compression along one prin
31、cipal axis of reinforcement. The test is performed at constant crosshead displacement rate. The test duration is limited to reduce any time dependent effects (creep, etc.). 4 Definitions and symbols For the purpose of this prestandard, the following definitions and symbols apply: 4.1 test temperatur
32、e, T temperature at the centre of the test piece 4.2 maximum flexural force, Fm highest recorded force in a flexural test on the test specimen when tested to failure 4.3 flexural stress, the nominal stress on the outer surface of the test specimen, calculated at mid span NOTEThis stress is conventio
33、nally calculated according to the simple beam theory, whose basic assumptions may not be met by ceramic matrix composite materials. 4.4 flexural strength, f,m maximum flexural stress applied to a test specimen that fractures during a flexural test 5 Apparatus 5.1 Test machine The machine shall be eq
34、uipped with a system for measuring the force applied to the test specimen. The system shall conform to grade 1 according to EN 10002-2. 5.2 Test jig The test jig is composed of two parts, linked to the fixed and mobile parts of the machine. It has two outer support rollers and one (three-point bendi
35、ng) or two (four-point bending) inner support rollers. The material of the jig and that of the rollers shall not react with that of the specimen, nor with the environment. The cylindrical rollers shall have a diameter of 4 mm to 10 mm. Their length shall be at least equal to the width of the specime
36、n. They shall be made of a material with a hardness at least equal to that of the specimen. The axes of the rollers shall be parallel to within 0,01 mm/mm. The outer rollers (three and four-point bending) and inner rollers (four-point bending) shall be free to rotate (see Figure 1). Licensed Copy: L
37、ondon South Bank University, London South Bank University, Tue Dec 12 05:52:12 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ENV 12788:1998 4 BSI 04-1999 Either two or three rollers, for three-point or four-point bending respectively, shall be free to pivot around an axis parallel to the longitudinal d
38、irection of the test specimen, in order to adapt to the non-parallelism of the upper and lower faces of unmachined test specimens (see Figure 1). The rolling and pivoting ability of the rollers shall not be affected by heating. The distance between rollers shall be in accordance to clause 6. The inn
39、er roller(s) shall be centred with respect to the outer rollers to within 0,2 mm. In the case of four-point bending a levelling system shall be used to ensure symmetrical loading of the test specimen. The performance shall not change because of heating. 5.3 Test chamber Gastight chamber which allows
40、 proper control of the test specimen environment in the vicinity of the test specimen during the test. The installation shall be such, that the variation of the load during the time of loading, which may occur due to parasitic effects (variation of pressure, seals, etc.) is less than 1 % of the rang
41、e of the load cell being used. 5.3.1 Gas atmosphere The gas atmosphere shall be inert to the specimen material and test jig under test conditions. 5.3.2 Vacuum chamber The level of vacuum shall not induce chemical and/or physical instabilities of the test specimen material and test jig. 5.4 Set-up f
42、or heating The set-up for heating shall be constructed in such a way that the variation of temperature of the test specimen which is between the outer support rollers is less than 50 C at test temperature. 5.5 Temperature measurement Thermocouples shall comply to EN 60584-1 and EN 60584-2. Alternati
43、vely, pyrometers or thermocouples which are not covered by EN 60584-1 and EN 60584-2 but which are appropriately calibrated can be used. 5.6 Data recording system A calibrated recorder shall be used to record force-time curve. The use of a digital data recording system combined with an analogue reco
44、rder is recommended. 5.7 Micrometers Micrometers used for the measurement of the dimensions of the test specimen shall be in accordance with ISO 3611. 6 Test specimens Recommended specimen dimensions are given in Table 1. These dimensions have been successfully used and take due account of the follo
45、wing factors: The amount of material under load shall be representative of the nature of the material and of the reinforcement structure. This sets minimum limits to the span and to the width and thickness of the specimen. In the case of flexural, as opposed to tensile testing, also the distribution
46、 of the longitudinal reinforcement through the thickness has to be considered. When this distribution is not symmetrical with respect to the neutral plane, care shall be taken to insure that it is similar between specimens. The thickness and the distance between the inner and outer roller(s) shall b
47、e chosen so as to avoid shear failure. This is achieved by setting a minimum limit to the ratio between the moment arm and the specimen thickness. A value of 10 is commonly used and translates into a minimum L/h ratio of 20 in three-point bending, and a minimum (L-Li)/h ratio of 20 in four-point ben
48、ding with Li=L/3. Other factors affecting the size and dimensions of the specimens are the type of the heating and of the loading system, as well as the size of the test chamber. Table 1 Recommended test specimen and span dimensions NOTEIf it is necessary to define test specimens of different dimens
49、ions, the conditions of clause 6 should be taken into account. 7 Test specimen preparation 7.1 Machining and preparation During cutting out, care shall be taken to align the longitudinal test specimen axis with one of the principal axes of reinforcement. Dimensions in millimeters 1D, 2D set the displacement rate on the test machine; record the force versus time; load the test specimen up to failure; adjust the displacement to fully unload specimen and jig; read load signal at temperature and under inert atmosp